The present invention relates to a method for producing ceramic material, said ceramic material itself, a basis for a dental restoration, which is made from said ceramic material, and the method for production thereof, and a dental restoration with said basis and a method for producing said dental restoration.
For ceramic materials often aluminum oxide and/or zirconium oxide is used, i.e. oxidic ceramic. When producing dental restorations, such as crowns, it is known to use ceramic material as a basis therefore in the place of for instance metal, that remains visible after applying cover layers, for instance of porcelain. Ceramic material is preferred, because this results in a better esthetic appearance of the dental restoration to be produced, than metal. The basis of a dental restoration is placed on for instance the remains of a tooth, i.e. a tooth stump, and as such forms the basis or carrier of a dental restoration. In connection with the considerable dental forces, to which the dental restoration is subjected, the basis therefor needs to have a sufficient strength, apart from the visually observable properties in connection with the cover layers to be applied to the basis and made from e.g. porcelain to obtain the aforementioned esthetic effect. Moreover ceramic material is more desirable than metal because of the higher biocompatibility thereof.
Several ceramic materials, especially for the basis of a dental restoration, and methods for producing the ceramic material, the basis and the dental restoration are respectively known.
The American U.S. Pat. No. 5,104,319 relates to flame spraying the ceramic material, which in essence comprises aluminum oxide, zirconium oxide, titanium oxide or combination thereof to produce the basis for especially a dental restoration. Here ceramic material in powder form is suspended in a carrier liquid and subjected to a flame spraying process on an underground, having the form of a dental remain, e.g. the form of a tooth stump. According to this method small quantities of material, which is based on silicate, are added to increase the density, which corresponds to the strength of the basis of ceramic material. The strength, which can be obtained is however insufficient in order to apply the ceramic material and the method, when producing the basis of a dental restoration. The density, which is achieved, is too low for this, and the corresponding porousness is too high, such that tear formation, leading to fracture, can occur. As a matter of fact, this porousness of especially the grains of the raw material for the ceramic material is most sensitive for the enormous dental forces, occurring when used as a dental restoration, and can lead to tear formation and fracture, although the tensions in the basis as a whole remain below the desired fracture strength.
Another known technique is the use of massive dental porcelain to produce the entire dental restoration. This however has for a drawback, that this material is hard to process in order to realize the occlusal surfaces accurately as a result of the hardness of this dental porcelain. When the obtained form of the dental restoration is less than optimum, and the restoration inhibits free movement of the jaw, this can lead to occlusal discrepancies and dislocation of the cranio mandibular complex. Therefore, when placing such restorations, often corrections have to be made in order to avoid this problem, which is inhibited by the hardness of dental porcelain. Furthermore this dental porcelain exhibits a high degree of shrink during baking, as a result of which the fit on the underground and therefore later upon the dental remains is unsure and can even vary as a result of variations in the degree of shrink. A bad fit can lead to the dental restoration coming loose or disturbance of the cranio mandibular complex. Further the use of a uniform colored block leads to a restoration with an appearance, which seems considerably less lifelike.
Also essentially pure aluminum oxide can be pressed dry and sintered. However, to obtain a desirable appearance of the restoration addition of pigments is necessary, which disrupt the sintering process. Therefore products based on this known technology have an insufficient strength, when pigments are applied, or an insufficiently natural appearance.
Another known technique is for instance pressing the ceramic material dry onto the underground to form a basis, sintering the material and process it to the desired shape, for instance by milling. The application of ceramic material is for instance by pressing it in a dry form. The ceramic material as raw material essentially comprises aluminum oxide, zirconium oxide and/or titanium oxide or mixtures thereof. These ceramic materials and methods have for a disadvantage, that a considerable and largely unpredictable shrink occurs when sintering or baking. Furthermore the strength of the used ceramic materials is insufficient, in particular for application as a basis for a dental restoration. Also here the porousness of the grains of the powder of the raw materials for the ceramic material is the cause. Moreover the variation in the degree of shrink, which is anticipated by oversize production with an average shrink as a starting point, leads to inaccuracy of the fit and therefore losses in production through rejection of individual products with an incorrect fit. Deviating fit is however only to be detected, after the underground is removed. This inhibits continuous automated production processes, where this underground could be used to be engaged by a processing machine, such as a mill. As certainty about the fit first has to be obtained, the underground, however, needs to be removed. Also for applying the cover layers on the basis for the dental restoration, this necessity to remove the underground is an inhibition.
With the invention it is intended to remedy the problems and disadvantages of all the above mentioned techniques, to which end a method is provided for production of ceramic material, and the ceramic material itself is provided. The ceramic material, that results from the method according to the present application can be used in production of the basis for a dental restoration and therefore in production of the dental restoration itself, but can also be used as a substitute for plastic filling material, which is for instance used to fill cavities. By the absorption of raw material of the ceramic material the glass component is strengthened, where the glass component also infiltrates the porous structure of the ceramic material. Through this process a substantially massive mass is obtained without any porousness, because of which the strength of the products produced with this ceramic material, such as the basis for a dental restoration, exhibit a sufficient strength. The glass component also adheres to grains of the ceramic material, which is for instance in a powder form, so that these grains are among themselves connected by the glass component. As such a massive product is formed, which through supplemental sintering for producing the basis for a dental restoration, is powdered. This can be achieved by grinding. When thereafter this powder is applied to an underground, corresponding to a tooth stump, in an arbitrary manner, by spraying, brushing, or otherwise, the glass component becomes fluid and fluid phase sintering occurs. As a result the shrink when baking the ceramic material while sintering this ceramic material to form for instance the basis for a dental restoration, is overcome by the glass component and the basis securely fits exactly on the underground, where the underground has a shape corresponding exactly to that of the form of the tooth stump. This certainty obviates the need to remove the underground in order to verify the fit, so that the underground can remain in the basis during subsequent processing steps.
The underground is often made from an oven proof material, to which the ceramic material of the basis for a dental restoration adheres. Preferably this oven proof underground can be formed from partially sintered, or chemically bound aluminum oxide and/or zirconium oxide or mixtures thereof in order to ensure, that the basis adheres well thereto. By subsequently removing the underground in a milling manner, it is secured, that the restoration will fit well, so that passages along the sides and further dental decay and cavities under the influence of bacteria will not occur. The ceramic material according to the present invention can, in comparison with known techniques, be sintered very fast, whereby the production process of the actual basis or the dental restoration as a whole is accelerated.